
export default {
    debounce(func, wait, immediate) {
        let timeout, args, context, timestamp, result;
        return function () {
            context = this;
            args = arguments;
            timestamp = new Date();
            const later = () => {
                const last = (new Date()) - timestamp;
                if (last < wait) {
                    timeout = setTimeout(later, wait - last);
                } else {
                    timeout = null;
                    result = func.apply(context, args);
                }
            };
            if (!timeout) {
                timeout = setTimeout(later, wait);
            }
            return result;
        };
    },

    /* 找到最近的触发滚动事件的元素
     * @param {Element} element
       * @param {Element} rootElement
       * @return {Element | window}
     */
    getScrollEventTarget(element, rootParent = window) {
        let currentNode = element;
        // bugfix, see http://w3help.org/zh-cn/causes/SD9013 and http://stackoverflow.com/questions/17016740/onscroll-function-is-not-working-for-chrome
        while (currentNode && currentNode.tagName !== 'HTML' && currentNode.tagName !== 'BODY' && currentNode.nodeType === 1 && currentNode !== rootParent) {
            const overflowY = this.getComputedStyle(currentNode).overflowY;
            if (overflowY === 'scroll' || overflowY === 'auto') {
                return currentNode;
            }
            currentNode = currentNode.parentNode;
        }
        return rootParent;
    },

    // 判断元素是否被加入到页面节点内
    isAttached(element) {
        let currentNode = element.parentNode;
        while (currentNode) {
            if (currentNode.tagName === 'HTML') {
                return true;
            }
            if (currentNode.nodeType === 11) {
                return false;
            }
            currentNode = currentNode.parentNode;
        }
        return false;
    },

    // 获取滚动高度
    getScrollTop(element) {
        return 'scrollTop' in element ? element.scrollTop : element.pageYOffset;
    },

    // 设置滚动高度
    setScrollTop(element, value) {
        'scrollTop' in element ? element.scrollTop = value : element.scrollTo(element.scrollX, value);
    },

    // 获取元素距离顶部高度
    getElementTop(element) {
        return (element === window ? 0 : element.getBoundingClientRect().top) + this.getScrollTop(window);
    },
    // 可视区域
    getVisibleHeight(element) {
        return element === window ? element.innerHeight : element.getBoundingClientRect().height;
    },
    getComputedStyle: document.defaultView.getComputedStyle.bind(document.defaultView)
};
